1. Field of the Invention
The efficiency of control parts that are used in high-pressure collection chamber (common rail) injection systems depends sharply and the fuel volume that because of the extremely high pressure prevailing in the common rail flows into an outflow-side fuel outlet when the supply line from the common rail is opened. The smaller this fuel volume and the fuel volume required to control the control part are, the greater is the efficiency that can be attained with a fuel injector. Besides high efficiency of an injector for direct-injection internal combustion engines, a compact design of such a structural component is of great importance.
2. Description of the Prior Art
German patent disclosure DE 198 35 494 A1 relates to a unit fuel injector used to deliver fuel to a combustion chamber of direct-injection internal combustion engines with a pump unit that serves to build up an injection pressure and to inject the fuel into the combustion chamber via an injection nozzle. The unit fuel injector has a control unit with a control valve, which is embodied as an outward-opening A-valve, and a valve actuation unit for controlling the pressure buildup in the pump unit. To create a unit fuel injector with a control unit that is simple in design and small in size, and in particular has a short response time, in the version of DE 198 35 494 A1 the valve actuation unit is embodied as a piezoelectric actuator.
In this version, a guide ring is supported axially displaceably in the interior of the transmission body. Also in the interior of the guide ring, a valve shaft is prestressed against the valve body by means of a U-shaped disk and a cup spring. The guide ring rests on the valve body by means of a flat seat. The flat seat can also be embodied by other forms of seat. The spring element acts on the guide ring and is braced on the transmission body. The spring element is embodied as a compression spring. The valve actuation unit and the control valve are disposed such that their respective longitudinal axes extend congruently. The control part assembly known from DE 198 35 494 A1 requires close tolerances, which are complicated to produce for technical production reasons, in order to adapt the diameters, in particular, to one another with extreme precision. The high demands in terms of tolerances made of the components dictate correspondingly expensive production with high engineering effort and stringent demands in terms of the precision measurements of the components in question.
The advantages attainable with the version according to the present invention are seen above all in the fact that the control part of the control valve is guided in two guides, which are located in separate bodies. As a result, from a production standpoint the guides can be produced with the required tolerances substantially more simply and hence more economically. The design of the injector in the proposed version can also be made simpler, since in comparison to versions known from the prior art, fewer moving parts are needed.
Embodying two diameter regions on the control part also makes a control part possible that closes cleanly; that is, the control part moves cleanly into its seat face that closes the nozzle inlet in the injector housing. The retraction motion is reinforced by a spring element, supported on the control part in a way that is secured against kinking, that is braced on a collar located in the interior of the injector housing.
By means of the two guide portions embodied by different diameter regions on the control part, more secure and very fast closing of the hollow chamber located on the leaking oil outlet side in the injector housing is achieved, and thus a loss of fuel volume can be avoided. This in turn considerably enhances the efficiency of the control part of the injector, received in independent guides, as proposed by the invention.
Since a control edge that seals off the hollow chamber between the two guide portions is embodied on the control part, one leaking oil connection suffices on the control part designed according to the invention, which is movable in two guides separate from one another. This allows more-economical production of the injector housing of the pressure-controlled, two-piece injector for common-rail use. Since it has been possible to reduce the number of moving parts considerably, an increase in the service life of the pressure-controlled injector is also attainable.